The invention relates to a brake pressure control valve as defined hereinafter. SAE paper 840 465 discloses a brake pressure control valve which incorporates both a brake pressure reduction valve and a pressure build-up valve. The brake pressure build-up valve comprises a valve chamber which has an inner valve seat and which is designed for connection to a pressure source, a valve member which is movable in the valve chamber and which is at least partially spherical in shape, a compensating piston coupled to the valve member and a seal which seals the compensating piston relative to the valve chamber and also a closing spring. The compensating piston and the valve member are oppositely influenced by the pressure from the pressure source and thus relatively minor force is required to raise the valve member from the valve seat. The disadvantage is that as the valve member is being raised from and moved back to this valve seat friction forces are produced between the compensation piston and its seal. These friction forces impede the smooth raising and lowering of the valve member and accordingly the smooth apportioning of brake pressures. Smooth apportioning of brake pressures is further impeded in that even minor lifting of the valve member results in large valve opening cross-sections.